The storage and distribution environment of commercial goods has been altered radically in the 1980s. With advances in computer technology leading to product miniaturization, products such as office equipment and electronic instrumentation are now stored at a much higher dollar density. In fact, it is not unusual for the value of goods in storage to exceed the value of the warehouse in which they are stored.
Many industries have been forced to consider alternatives to conventional, highly flammable, expanded plastic packaging. The U.S. Navy has expressed a keen interest in the use of materials that will reduce the scale and hazard of shipboard fires. Moreover, requirements for rapid deployment of supplies and hardware have made high density warehousing of packaged goods a way of life for all branches of the armed forces.
Polyurethane foams are excellent packaging materials because of their cushioning ability. Moreover, items to be packaged can be completely encapsulated in protective polyurethane foam with two-component foaming equipment. An advantage of such foaming equipment is its reasonable cost: the equipment need only be capable of handling a polyisocyanate component (the "A-side" polyurethane resin) and a polyol component (the "B-side" polyurethane resin). Equipment capable of handling more than two components is much more expensive. The present invention is not limited to packaging foams but could also be practiced in the entire arena of polyurethane technology including uses for insulation, structural and decorative, elastomers, coatings, etc.
Carbohydrates, because they are charring agents, give polyurethane foams excellent fire-retardant properties when used in conjunction with other fire-retardant chemicals. Unfortunately, carbohydrates heretofore could not be mixed with polyols to form a phase stable B-side polyurethane resin. As a result, expensive foaming equipment capable of servicing more than two component streams had to be used.
The resolution of this problem is particularly difficult because the compositions one is led to in developing a polyurethane foam containing a fire-retardant carbohydrate additive are ordinarily much different from the compositions one is led to in developing a polyurethane foam which will have satisfactory properties for other purposes, such as good cushioning for packaging.
Numerous patents disclose the use of unmodified carbohydrates as a substitute for a conventional polyol to prepare polyurethanes. Illustrative are U.S. Pat. Nos. 4,515,638; 4,417,998; 4,400,475; and Re. 31,757. While such polyurethanes may be foamed on conventional foaming equipment, the use of a carbohydrate in the absence of other conventional polyether or polyester polyols selected to produce flexible, cushioning foams results in a foam which is too brittle for commercial use. U.S. Pat. No. 4,404,294 suggests reacting a polyisocyanate in the presence of a polyol with water in which carbohydrates have been dissolved. The water-carbohydrate-polyol mix is not a compatible mix. Such a reaction would have to be carried out on foaming equipment capable of servicing three component streams. Alternately, polyurethane foams which are formed from aqueous slurries containing carbohydrates, such as described in U.S. Pat. No. 4,237,182, also require more expensive foaming equipment.
Numerous other patents disclose the addition of polysaccharides having a high degree of polymerization, such as starch and cellulose, to polyurethane resins. Illustrative are U.S. Pat. Nos. 3,956,202; 3,004,934; 3,957,702; 4,374,208; 4,458,034, 4,520,139; and 4,521,544. In all cases, the polysaccharide cannot be dissolved in the polyol component and must be processed as a solid. U.S. Pat. No. 3,956,202 to Iwasaki, which deals with rigid polyurethane foams, suggests reactions by which a polysaccharide might be made more soluble and more dispersible, but in the invention disclosed therein these compounds do not dissolve--they merely become more easily dispersible as solids. Other patents which disclose polyurethanes prepared from modified carbohydrates, such as U.S. Pat. Nos. 3,600,338 and 3,165,508, provide no suggestion as to how the carbohydrates may be solubilized in the polyol component. In all these cases, equipment servicing more than two components is required in order to prepare the desired foams.
Finally, numerous patents disclose polyurethanes prepared from modified carbohydrates in which the carbohydrates have been modified so that substantially all of hydrated carbons have been reacted, but such modified carbohydrates are of little use as char-forming fire-retardant agents. Illustrative of these disclosures are U.S. Pat. Nos. 3,004,934; 3,956,202; 3,957,702; 4,374,208; 4,458,034; 4,520,139; and 4,521,544.
Accordingly, it is an object of the present invention to provide a polyurethane foam which has cushioning properties satisfactory for use, for example as a packaging or insulation material, and contains a carbohydrate modified to a minimum extent as a fire-retardant additive.
An additional important object of the present invention is to provide a method of making such a foam on foaming equipment which is capable of servicing only two component streams.
A still further object of this invention is to provide a polyurethane resin for making such a foam, which resin is a single phase solution comprised of a polyol and a carbohydrate. Insofar as this applicant is aware, nothing in the prior art suggests how these objects can be achieved.